1. Field of the Invention
The present invention is in the field of equipment and devices related to manufacturing heart valves to be used in cardiac surgery. More specifically, the present invention is directed to molds in which biological membranes are shaped into the configuration of replacement heart valves to be used in cardiac surgery. The present invention is also directed to a sizer for measuring the valve annulus of a patient so as to determine the appropriate size of mold to be used in that patient.
2. Brief Description of the Prior Art
Heart valve reconstruction using patient""s own tissue (autologous tissue) or cadaver (homologous) or animal (heterologous) tissue is not new. As is known, heart valves (aortic, pulmonary, tricuspid or mitral) function essentially as check valves which operate hemodynamically in synchronization with the pumping action of the heart, allowing blood flow in a downstream direction and blocking flow in the opposite or upstream direction. One of the important requirements in valve reconstruction using autologous, homologous or heterologous tissue is the ability to produce a valve form which is as close to the natural valve as possible in order to serve its function effectively as a replacement valve. In addition it is important to fabricate the replacement valve accurately to fit any specific patient, quickly and effectively within the shortest possible time frame.
Among the tissues used in these molds for fabricating replacement heart valves, autologous tissue has been given special consideration because of its low cost, availability from the patient who is undergoing the open heart surgery operation, and relative ease of handling. For the ultimate replacement valve design, however, the nature of the mold in which the valve is formed is also of great importance, and over the years, a number of molds or templates were introduced to fabricate replacement heart valves from autologous, homologous or heterologous tissue. As noted above, the replacement valve should mimic the natural heart valve as close as possible. As a summary of prior art valve design, the following developments are noted.
Duran et al. Journal of Thoracic and Cardiovascular Surgery, 1995, August have developed a valve mold comprising 3 bulges or lobes in a rectangular plastic container. The bulges serve to reproduce the 3 leaflets of the aortic valve. A strip of autologous pericardium is laid over the bulges and an opposite mold to the 3 bulges is held over the pericardial strip whilst immersed in a solution containing a tanning agent that fixes the pericardium strip in the shape dictated by the mold. After fixation, the pericardial strip is removed and is held in the surgeon""s hand for trimming along the impression left by the mold. Trimming of the unsupported autologous tissue, which is flimsy and thus difficult to handle results in certain inaccuracy in tracing the path marked by the mold.
Love et al. Journal of Heart Valve Disease 1998, Volume 7, No. 1. have designed a valve mold with a concept similar to the above-described, involving a positive and a negative template and having an added feature of a xe2x80x9ccutterxe2x80x9d to trim the excess autologous tissue while the tissue is held in the mold. The Love et al. Journal of Heart Valve Disease 1998, Volume 7, No. 1. valve mold is constructed primarily of metal which makes the overall device heavy and relatively bulky.
Generally speaking, the two main problems which can be identified in current state-of-the-art valve mold design are:
(i) Difficulty in trimming the excess pericardium effectively, accurately within shortest possible time, and
(ii) the overall design of the valve mold is heavy and or bulky.
In light of the foregoing, there is a need in the state-of-the-art for a mold design for valves that offers greater precision and reproducibility to overcome the above-stated problems, and is cost effective in manufacturing.
Written descriptions of examples of prior art valve mold design and of the procedures employed by the surgeon in the operating room are found in U.S. Pat. Nos. 5,344,442; 5,425,741; 5,489,298; 5,500,015; 5,509,930; 5,522,885; 5,531,784; 5,531,785; 5,571,174; 5,584,878; 5,588,967; 5,609,600; 5,612,885; 5,653,749; 5,662,705; 5,697,382, and 5,716,399. Many of the valve constructions described in these patents include valve stents that are needed to support the molded tissue to form the replacement valve.
The following scientific publications also describe or relate to the use of human or animal membranes for heart valve replacement.
1. Senning A. Fascia Lata Replacement of Aortic Valves (unstented, unshaped) Journal of Thoracic Cardiovascular Surgery 1967, 54:465-470;
2. Edwards et al. Mitral and Aortic Valve Replacement with Fascia Lata on a Frame (stented, unshaped) Journal of Thoracic Cardiovascular Surgery 1969, 58:854-858;
3. Yacoub et al Aortic Valve Replacement Using Unstented Dura or Calf Pericardium: Early and Medium Term Results in Biologic Bioprosthetic Valves (unstented,unshaped) Proceedings of the third international symposium. In: Bodnar E, Yacoub m (ed) Yorke Medical books, New York 1986:684-690;
4. Batista et al. Clinical Experience with Stentless Pericardium Aortic Monopatch for Aortic Valve Replacement (unstented, unshaped) Journal of Thoracic and Cardiovascualr Surgery 1987:93:19-26;
5. Duran et al. From Aortic Cusp Extension to Valve Replacement with Stentless Pericardium (unstented, shaped) Annal Thoracic Surgery, 1995, 60:S428-32;
6. Duran et al. Aortic Valve Replacement with Freehand Autologous Pericardium (unstented, shaped) Journal of Thoracic and Cardiovascular Surgery 1995 August;
7. Duran et al. Aortic Valve Replacement with Autologous Pericardium (unstented, shaped) Surgical Technique Journal of Cardiovascular Surgery 1995, 10:1-19;
8. Love Autologous Pericardial Reconstruction of Semilunar Valves Journal of Heart Valve Disease 1998, Vol 7 No. 1;
It is an object of the present invention to provide a mold that is suitable for rapidly forming a substantially flat biological membrane into a configuration that can be quickly and accurately trimmed to provide a replacement heart valve.
It is another object of the present invention to provide a mold that satisfies the foregoing objective and allows formation of the replacement heart valve with high accuracy and repeatability.
It is still another object of the present invention to provide a mold that satisfies the foregoing objectives and is relatively easy and economical to manufacture and handle.
It is yet another object of the present invention to provide a set of sizers to measure accurately the diameter of the aortic valve annulus of the patient in order to determine and select the appropriate size of mold to be used in that particular patient.
The foregoing and other objects and advantages are attained by a pair of templates provided to form a mold for substantially flat biological membranes such as a pericardium, peritonium or pleura, to shape the membrane into a configuration that, after trimming of excess tissue, is adapted for forming a replacement aortic, pulmonary, tricuspid or mitral heart valve. Each template of the pair has three members joined to another laterally, with each member configured to form, together with its mating member, the mold for one leaflet or cusp of the replacement heart valve. The first or negative template has concave surfaces for each member and the second or positive template has convex surfaces which mate with the concave surfaces of the first template. Each of the templates is made of thin, shell like material and has thin edges that makes it easy to cut with a surgical knife close to the mold. The biological membrane is placed between the mating convex and concave surfaces of the two templates assembled to one another to form the membrane into the configuration of the three leaflets of the replacement heart valve. The templates of the mold are provided with apertures to allow a liquid composition to percolate to the membrane and affix the membrane in the configuration defined by the mold.